此题一开始用暴力做，后来发现斜着走的时候其实暴力不太好写，于是改用搜索写了
1 #include <iostream> 2 #include <stdio.h> 3 #include <memory.h> 4 using namespace std; 5 6 char a[110][110]= {0}; 7 int down[110][110]= {0}; 8 int up[110][110]= {0}; 9 10 int cnt[110][110][4]= {0}; 11 int n; 12 int dx[4]= {-1,1,-1, 1}; 13 int dy[4]= {-1,1, 1,-1}; 14 int dfs(int curx,int cury,int num) 15 { 16 if(curx<0 || cury<0 || curx>=n || cury>=n) 17 return 0; 18 int &ans=cnt[curx][cury][num]; 19 if(a[curx][cury]=='#') 20 return ans=0; 21 return ans=1+dfs(curx+dx[num],cury+dy[num],num); 22 } 23 24 25 int getMax() 26 { 27 int ans=0; 28 for(int i=0; i<n; i++) 29 for(int j=0; j<n; j++) 30 { 31 ans=max(ans,down[i][j]+up[i][j]-1); 32 } 33 return ans; 34 } 35 36 int main() 37 { 38 freopen("in.txt","r",stdin); 39 40 while(scanf("%d",&n),n) 41 { 42 memset(down,0,sizeof down); 43 memset(up,0,sizeof up); 44 memset(cnt,0,sizeof cnt); 45 for(int i=0; i<n; i++) 46 scanf("%s",a[i]); 47 48 for(int i=0; i<n; i++) 49 for(int j=0; j<n; j++) 50 { 51 if(a[i][j]=='#') 52 { 53 up[i][j]=down[i][j]=0; 54 55 } 56 else 57 { 58 up[i][j]=down[i][j]=1; 59 if(i!=0) 60 up[i][j]=up[i-1][j]+1; 61 if(j!=0) 62 down[i][j]=down[i][j-1]+1; 63 } 64 } 65 66 int ans=0; 67 ans=max(ans,getMax()); 68 69 memset(down,0,sizeof down); 70 memset(up,0,sizeof up); 71 for(int i=n-1; i>=0; i--) 72 for(int j=n-1; j>=0; j--) 73 { 74 if(a[i][j]=='#') 75 { 76 up[i][j]=down[i][j]=0; 77 } 78 else 79 { 80 up[i][j]=down[i][j]=1; 81 if(i!=n-1) 82 up[i][j]=up[i+1][j]+1; 83 if(j!=n-1) 84 down[i][j]=down[i][j+1]+1; 85 } 86 } 87 88 ans=max(ans,getMax()); 89 90 //--------------------------- 91 memset(down,0,sizeof down); 92 memset(up,0,sizeof up); 93 for(int i=0; i<n; i++) 94 for(int j=n-1; j>=0; j--) 95 { 96 if(a[i][j]=='#') 97 { 98 up[i][j]=down[i][j]=0; 99 } 100 else 101 { 102 up[i][j]=down[i][j]=1; 103 if(i!=0) 104 up[i][j]=up[i-1][j]+1; 105 if(j!=n-1) 106 down[i][j]=down[i][j+1]+1; 107 } 108 } 109 110 ans=max(ans,getMax()); 111 //------------------------------- 112 memset(down,0,sizeof down); 113 memset(up,0,sizeof up); 114 for(int i=n-1; i>=0; i--) 115 for(int j=0; j<n; j++) 116 { 117 if(a[i][j]=='#') 118 { 119 up[i][j]=down[i][j]=0; 120 } 121 else 122 { 123 up[i][j]=down[i][j]=1; 124 if(i!=n-1) 125 up[i][j]=up[i+1][j]+1; 126 if(j!=0) 127 down[i][j]=down[i][j-1]+1; 128 } 129 } 130 131 ans=max(ans,getMax()); 132 //-------------------------------------------------- 133 134 for(int i=0; i<n; i++) 135 for(int j=0; j<n; j++) 136 { 137 for(int num=0; num<4; num++) 138 { 139 dfs(i,j,num); 140 } 141 } 142 143 for(int i=0; i<n; i++) 144 for(int j=0; j<n; j++) 145 { 146 ans=max(ans,cnt[i][j][0]+cnt[i][j][2]-1); 147 ans=max(ans,cnt[i][j][0]+cnt[i][j][3]-1); 148 ans=max(ans,cnt[i][j][1]+cnt[i][j][3]-1); 149 ans=max(ans,cnt[i][j][1]+cnt[i][j][2]-1); 150 } 151 152 cout<<ans<<endl; 153 } 154 return 0; 155 }